The decision stemmed from a lawsuit filed by 11 states and environmental groups that argued federal regulators ignored the effects of carbon dioxide emissions when calculating fuel economy standards for light trucks.

Filed last year, the suit sought to force the National Highway Traffic Safety Administration to recalculate its mileage standards from scratch, with carbon dioxide emissions taken into account as a major factor in the agency's analysis.

Gov. Arnold Schwarzenegger said Thursday that California won't back down from the lawsuit — but will stick to its plan to put tougher standards in place by the 2009 model year despite protests from the auto industry.

Last week, California sued the U.S. Environmental Protection Agency, seeking to force the agency to decide whether California can enact the country's first emissions standards for cars and light trucks.